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I'm not sure how you think Convergence is going to remove the central trust of DNS: If the attacker has control of your DNS records then every one of the notaries is going to go to the wrong IP address to check the certificate and they'll all see the same (wrong) one.Notary requests use TLS too: If an attacker redirects my requests to other (untrusted) notaries my client will complain because it has the (self-signed) certs of the notaries cached. I can buy two or more servers in different counties, install the notary server on them, copy&paste the cert of the notaries in my client, and from that moment on Convergence works and my TLS connections are secure.
> Convergence also requires client support on all the clients before you can stop using CA-signed certificates, which isn't going to happen quickly.
Clients that use Convergence are effectively CA free from the moment they install it. The others can follow incrementally.
> A CA (or someone who bought an intermediary CA certificate from an existing CA) could set up the thing I described in a matter of hours and henceforth anybody who needs a domain validated TLS certificate could get one instantly, securely and for free by just adding a DNS record and visiting that website.
Notary certs are self signed. A browser vendor could set up a few notary servers that use certs they signed themselves and ship with them by default. Browser vendors already ship with the CA certs, so instead of the CA certs they would ship with their own cert that signed the ones the notaries use. If you don't trust them use your own notaries no problem. Everything works like before. I just think it's an awesome idea.